Contents lists available at ScienceDirect Industrial Crops & Products journal homepage: www.elsevier.com/locate/indcrop Kinetic parameters of the oxidation reaction of commercial biodiesel with natural antioxidant additives Érica Signori Romagnoli a , Dionísio Borsato a, ⁎ , Lívia Ramazzoti Chanan Silva a , Letícia Thais Chendynski a , Karina Gomes Angilelli a , Edmilson Antônio Canesin b a State University of Londrina, Chemistry Department, Laboratory of Fuels Research and Analysis, Caixa Postal: 10.011, CEP: 86057-970, Londrina, Paraná, Brazil b Chemistry Department, Federal Technological University of Parana, Marcílio Dias, 635, Apucarana, Paraná, Brazil ARTICLE INFO Keywords: Oxidative stability Experimental design Apparent activation energy ABSTRACT Biodiesel in Brazil is obtained through the mixture of vegetable oils and animal fats. However, some of those raw material sources have characteristics that are more susceptible to oxidation. As an alternative to reduce the speed of the onset of the oxidation reaction, spices are added to biodiesel. The oxidative stability was analyzed through the period of induction using the Rancimat ® method. This study evaluated the effects of antioxidant extracts from senna leaves, blackberry fruits and hibiscus flowers mixed to commercial biodiesel through the determination of kinetic parameters, as well as investigating possible linearity deviations from the Arrhneius equation. It was possible to verify that the rate constant values were smaller when compared to the control sample; lower values were observed for mixtures with higher proportions of hibiscus flower extract. The acti- vation energy values did not present linear behavior, and some tests presented values above the control sample, showing that the addition of antioxidants can significantly alter this parameter. Sub-Arrhenius behavior was observed for the sample containing the binary mixture of senna leaves and hibiscus flowers and for the control; however, sample containing only senna leaf extract presented super-Arrhenius behavior. 1. Introduction Commercial biodiesel is obtained through the mixture of vegetable oils – such as soybean, sunflower, palm oil - and animal fats - such as tallow, poultry fat and lard, depending on the production region and the sources of raw materials available (Orives et al., 2014; Chendynski et al., 2016). Since biodiesel is produced with unsaturated carbon chains, it may be less chemically stable than diesel (Angilelli et al., 2017). Oxidation reaction in biodiesel occurs between esters of unsaturated fatty acids – molecules that are very reactive in the presence of oxygen from the environment, resulting in products such as aldehydes, ketones, polymers, acids, peroxides, among others. Therefore, oxidation can compromise the quality of the biodiesel and affect its performance as fuel, due to the changes that such molecules cause in its properties (Pullen and Saeed, 2012; Buosi et al., 2016). Currently, the most largely used substances to inhibit the oxidative degradation reactions are synthetic antioxidants, which are used in the food industry and other sectors. However, they present some negative factors such as their toxicity to humans and their low biodegradability (Carocho et al.,2014; Knothe et al., 2015; Spacino et al., 2015). The use of natural antioxidant substances derived from plants and fruits can be a good alternative to synthetic antioxidants, since anti- oxidant substances such as tocopherols, phenolic compounds, flavo- noids, terpenes, and carotenoids are extensively found in several plants in many different parts, from roots to leaves and even fruits. All natural antioxidants can be extremely useful in preventing biodiesel oxidation, especially phenolic compounds, since they present a hydroxyl group with more active electrons than those in fatty acid esters (which are a constituent of biodiesel). However, despite the potential advantages that natural antioxidants offer in enhancing the oxidation resistance of biodiesel, very few studies have sought to demonstrate their efficiency in inhibiting oxidation reaction, with little work on developing blends of natural antioxidants with commercially available biodiesel (Coppo et al., 2014; Spacino et al., 2015). By using the Rancimat ® method for determining the oxidative sta- bility at different temperatures, several data can be obtained regarding electrical conductivity and the oxidation reaction induction period for biodiesel, showing the effects the antioxidant substances induce on the biofuel. From such data, the rate constant (k), and activation energy https://doi.org/10.1016/j.indcrop.2018.08.077 Received 5 February 2018; Received in revised form 23 August 2018; Accepted 29 August 2018 ⁎ Corresponding author. E-mail addresses: dborsato@uel.br (É.S. Romagnoli), dborsato@uel.br (D. Borsato). Industrial Crops & Products 125 (2018) 59–64 0926-6690/ © 2018 Elsevier B.V. All rights reserved. T